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Patented July 29; 1952 Nini Drawing. Application Jaif'ai'yiafiao; I f u vrialjNo. 1 39,320., ,In the Netherlands January 'A e ,The preparation of lacta'r'ns" Beckmanns parts ,by'vJeight of oxime and Aacidfj at temperaf tures "of approximately 80 to 130"V C.` In order 'to isolatel the 'lactamsfrom this mixture "of rear-` rangement, the acid is neutralised preferably ink aqueous solution. The lactams aresoluble in Water, lbut .are almost completelylsyeparated" in concentrated vsolutions of lneutral salts. It' is,

tlfie'refore,l desirable` to use the vneutralising agent" together 'with only such an' amount of Water that,v

afterl neutralisation', i a.' saturated y salt solution' is I obtained. The'lactarns thus` .separate in form of a Water-'containing oily layer, and `only a small" amount` which can be recovered With organic sol-V vents, remains dissolvedl in the salt solution. The" pure lactams are obtained by distillation of the water-containing products.'

','The neutralisation has hitherto been vconducted byallovving the mixture of rearrangement to'flovv' in ice-Waterand neutralising the diluted sulfuric acid in the cold, or'by adding thernix'ture of arrangementinl the cold and lvvith good 'stirring'AV to an aqueous csolutionof the neutralisingagent j until thev acid Was neutralised. In both c'as esa`v lossof lactam may easily occur due tof the ifa-ct' that the said .subz'sta'nces'Y arereadily decomposed in 4s]trengly'"acid solutions aswell as inLalk line.

solutions. This decomposition 'is yespeciall markabledat elevated ytemperatures and hl1V prolongated neutralisationtime's. 'Both methods, f

thereforarequire not only good cooling but 'also the maintenance of loW temperatures such as can only be obtainedby the use of cooling brines. It may be more convenient to performithe neutralisationin a continuous manner, i. e'. to' react the aqueous neutralising agent and the Amixture ofirearrangement-'in aneutral mediumb-y feeding both components into the reacted aqueousneutralising mixture While cooling andstirring Well.

As the rearrangement Yrnixti'ireis' very viscous, itv does not at once distribute'itself throughout the aqueous neutralisation mixture, but forms local zones which arevstrongly acid and over-heated and.Wherendeempostion0f the. latamfmav occu-r..f1n,the last mentioned neutralisation process, the amount of lactam inthe neutralisationJ the vla'ct'ams' withY considerable lexcellent yields if the*'continuousv preparation :thereof is performed'infsuch manner that the neutral salt solutionwhich is obtainedand separated in the "f neu'tralisationv process; is recycled `or fed back into the space-in which occurs neutralisationof the' products obtainedbythe rearrangement of cyclicl oximes With the aid of strong sulfuric acid'or oleum; The amount of the salt solution fedv back should be at least equaltoor 'a multiple of the aqueous neutralising-medium employed inja like time interval.A

To this'end, hesalt solution obtained in the neutralisationgprocess, `after having been thoroughly `freed frorrritslactam content, 'is fed into the aqueousneutralisation medium in the zoneo f neutralisation' or immediately before said zone, whereupon said mixture and the lactam-containing lrearra'ngement'product are interacted in as fineairdisp'ersion as'possible. The neutralised mixture thereby may flow off from the neutralisation zone While still hot, Without impairing the yield of lactam. Cooling need not be effected With cdoling brin-since mere cooling Water is suic'ient." It is advantageous to use( the salt solution which has been thoroughly7 freedY from its laetam content, in a precooled state for dilutingv the neutralisation components. The ne dispersi'on" and intimatejmixture of the lcomponents attained 'byf vigourously stirring in a pace` 'or yby' bringingtogether the liquid components in jv a "'inely fdistributed .state and' atr highfs'r'ieed, orflex'amplexby means o f nozzles or Y v By the provision of a small l'neutralisation space portic'in v,o'f l'ajctam inthe neutralisation mixture,

the` decomposition "of vthe lactams is prevented in asubstantial degree. The time during ywhich thereactantsfstay inthe lzone lof neutralisation should 'be shorten'ed'las much 'as possible. n The higher Vthe temperature 'of neutralisation, `which maybe raised upto the boiling point ofthe mixture, thev shorter V.should be this time, i. e. the faster f the separated crude lactam should be removed'from the space of reaction. Generally the time during which tha-reactants remain in said space, shouldznot exceed 3 tol 10 minutes.

The neutralising agents. are preferably such alkaline substances as together with sulfuric acid Will give salts which are readily soluble in water,y

that is to say, lwhich are liable to form highlyconcentrated solutions. It should :be avoided 'as cyclohexanone oxime with oleum, having a teniperature of about 50 C., and a mixture of 40 parts of 14.5% aqueous ammonia having a temperature of 20 C. with 40 parts of a saturated ammonium sulfate solution coming from the neutralisation process and having a temperature of 30 C., flow continuously together per hour in an Orix-Mixer." The neutralisation product ows I into a separating vessel at a temperature of 80 ammonium sulfate, I preferablyuse lan aqueous ammonia solution containing 13 to 15% of ammonia. In the same manner, the neutralisation may be performed with sodium or potassium hy-q `droxide solutions having a hydroxide content of Y 20 to 25%. In this case a saturated solution of sodium or potassium sulfate originating from the same neutralisation, is fed back into the space of neutralisation.

The pH value of the neutralisation mixture should be kep-twin the range between 3 and 8, preferably at an average value of about 6.

The mixture flowing away from the neutralisation zone'may be separated, before or after 4cooling, into the oily.A crude lactam, and an approximately or completely saturated sulfate solution. From the crude lactam a pure lactam is obtained by vacuum distillation, in a yield of approximately 93% calculated on the lactam contentY of the rearrangement mixture.

The process described inthe foregoing specification is especially well suited for the separation of lactams obtained from cyclic oximes having 6 and more carbon atomsin their ring. The lactams obtained from oximes with 6 -to 11 carbon atoms, are preferred. Examples for such lactams and the lrelated oximes are caprolactam and cyclohexanone oxime, oenantholactam and suberone oxime, w-aminooctylic acid lactam and cyclooctanone oxime w-aminononylic acid lactam and cyclononanone oxime, w-amino-decylic acid lactam and cyclodecanone oxime,rwaminounde cylic acid lactam and cycloundecanone oxime.

The parts indicated in the following examples are parts by volume.

Y Eample 1 18.6 parts of a product obtained by the reaction of cyclohexanon-e oxime with oleum and 40 parts of a 14.5% aqueous ammonia solution and 80 parts of a saturated ammonium sulfate solution, derived from the neutralisation process, are allowed to flow per hour into a vessel which is provided with a stirrer and is externally cooled and has a volume equivalent to parts, but is.

reduced by means of a syphon over-flow to van effective volume equivalent to 2.5 parts. The neutralisation product ows through Ithe over-flow into a separating vessel at a temperature of 75 C. and with a pH value of 6. From the separating vessel 15.8 parts of the vcrude lactam (specific gravity 1.07 at C.) and ammonium sulphate solution (specific gravity 1.241 at 20 C.) lare drawn oi per hour.. The sulphate solution is extracted with an organic solvent and the whole of the crude lactam is distilled in vacuo. Pure caprolactam is obtained in a yield of 92.5%.

Example 2 19V-parts oftthe'mixture obtained by treating C. and a pH 7, from which crude lactam is drawn off at an hourly rate of 16 parts. By vacuum distillationv the pure caprolactam is obtained in a 93% yield. rIfhe separated ammonium sulfate solution is partly fed back to neutralisation.

VExample 3 48 parts vof the rearrangement product obtained from suberon oxime with oleum, 100 parts oi' yaqueous ammonia solution (15%) and 100 parts of the ammonium sulfate solution fed back from the neutralisation are mixed intimately in the manner described in Example 2. Themixture which flows into a separating vessel, has a temperature of C. and a pH of 6.5. From said vessel, crude lactam is drawn oil at an hourly rate of 41 parts, with a specific gravity of 1.065 at 20 C. The crude lactam is distilled in vac-uo, and the pure oenantholactam is obtained in a yield of 90%.

What I claim is:

In a process for separating lactams from the mixture obtained by Beehmanns rearrangement of cyclic oximes with strong sulphuric acid, the steps of continuously delivering into a neutralizing vessel the rearrangement mixture and a neutralizing agent in aqueous solution and of the type to form with the sulphuric acid a water soluble salt, continuously drawing oif the resulting neutralized mixture from said neutralizing vessel at a rate to maintain a substantially constant amount of liquid lin said neutralizing vessel, said neutralizing agent being delivered to said vessel in amounts only suflicient to neutralize substantially the acid in the rearrangement mixture in said vessel and to maintain thereby the pH of the neutralized mixture drawn oil from said vessel at an average value of about 6, separating in the drawn olf neutralized mixture the lactam from the neutral salt solution produced by the reaction of the neutralizing agent and the sulphuric acid, and continuously returning to said neutralizing Vessel the separated neutral salt solution in amount to maintain the solution drawn off from said vessel substantially saturated with the neutral salt.

KURT KAHR.

REFERENCES CITED The following references are of record in the i'lle of this patent: Y

UNITED STATES PATENTS OTHER REFERENCES Boundy et al.: CIDS Target No.' 22/517, Item No. 22, file No. XXVI-53 (530), Manufacture 01 Caprolactam, 6 pages. 

